Calcium silicate insulating material containing alumina silica microspheres

ABSTRACT

An asbestos free, calcium silicate insulating material suitable for use in the casting of molten non-ferrous metals, and suitable for use in applications where a fire resistant, heat insulating, electrical insulating, and corrosion resistant material is desirable. The calcium silicate insulating material is produced by combining lime, a siliceous component, alumina silica microspheres, wollastonite and organic fibrous material in the presence of water to form a slurry. The slurry is then placed under steam pressure, to react the lime, siliceous component and water, dried, and heat treated if necessary.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit and is a div. of U.S. patentapplication Ser. No. 09/742,164 filed Dec. 20, 2000 now abandoned, andentitled Calcium Silicate Insulating Material Containing Alumina SilicaMicrospheres.

FIELD OF THE INVENTION

The present invention relates generally to improved insulatingheat-resistant materials containing alumina silica microspheres andmethods of producing such materials. The present invention furtherrelates to such materials containing alumina silica microspheres andmethods wherein the resulting materials produced are suitable for use inthe casting of non-ferrous metals such as aluminum and similar metals.

BACKGROUND OF THE INVENTION

A variety of insulating heat-resistant materials suitable for use incasting of non-ferrous metals are well known in the prior art. Of theinsulating heat-resistant materials utilized in the process of castingnon-ferrous metals that are known in the prior art, calcium silicatebased materials have proven to be of particular utility because of theirsmall heat capacities, high heat insulating capability and non-wettingproperties in contact with molten non-ferrous metals.

Calcium silicate based insulating materials employed in casting ofnon-ferrous metals have typically been of the tobermorite-type matrixstructure and xonotlite-type matrix structure of calcium silicateinsulating material.

A fundamental tobermorite-type matrix structure of calcium silicateinsulating material is disclosed in U.S. Pat. Nos. 4,111,712 and4,128,434 to Pusch. This fundamental tobermorite type matrix structureof calcium silicate insulating material is produced by combining, asource of calcium, such as hydrated lime or quick lime, a source ofsiliceous material, such as silica, diatomaceous earth, silica fume,colloidal silica, or other suitable oxides of silicon, fibrouswollastonite and an organic fiber, such as kraft made from wood pulp, inthe presence of at least one part by weight water per part by weight ofthe forgoing combined materials, to form an aqueous slurry. The aqueousslurry is then poured into a mold where the excess water is pressed outof the mixture to form an uncured shape, typically a sheet. The uncuredshape is then placed in an autoclave where it is heated under steampressure of about 100 psi. The shape is then oven dried to about 250degrees Fahrenheit, and subsequently heat treated to above 500 degreesFahrenheit. Finally, the resultant tobermorite type calcium silicateinsulating material is cut or machined to the appropriate dimensions foruse in the particular application.

As with the tobermorite-type matrix structure of calcium silicateinsulating material, the xonotlite-type matrix structure of calciumsilicate insulating material is known in the prior art. A fundamentalxonotlite-type matrix structure of calcium silicate insulating materialis produced by combining a source of calcium, such as hydrated lime orquick lime, a source of siliceous material, such as silica, diatomaceousearth, silica fume, colloidal silica, or other suitable oxides ofsilicon, fibrous wollastonite, an organic fiber, such as kraft made fromwood pulp in the presence of at least one part by weight water per partby weight of the forgoing combined materials in an autoclave under about200 psi steam pressure. The resultant aqueous slurry is then pressed ina mold and dried in an oven.

Alternatively, the fundamental xonotlite-type matrix structure ofcalcium silicate insulating material may be produced by mixing a sourceof calcium, such as hydrated lime or quick lime, a source of siliceousmaterial, such as silica, diatomaceous earth, silica fume, colloidalsilica, or other suitable oxides of silicon, fibrous wollastonite, anorganic fiber, such as kraft made from wood pulp in the presence of atleast one part by weight water per part by weight of the forgoingcombined materials in the presence of water to form an aqueous slurry.The aqueous slurry is then poured into a mold where the excess water ispressed out of the slurry to form an uncured shape, typically a sheet.The uncured shape is then placed in an autoclave where it is heatedunder steam pressure of about 200 psi. The shape is then oven dried.

Finally, the resultant xonotlite type calcium silicate insulatingmaterial is cut or machined to the appropriate dimensions for use in theparticular application.

Although these fundamental tobermorite type and xonotlite type calciumsilicate insulating materials have been found to be suitable for use inconnection with the casting of relatively low melting point non-ferrousmetals and in other uses, certain shortcomings of these insulatingmaterials have become apparent in application. In producing an optimalcalcium silicate insulating material, it is desirable that theinsulating material have reduced density, increased strength, improvedthermal insulating properties, be homogeneous throughout with minimizedthermal shrinkage. Of particular importance for calcium silicateinsulating material utilized in connection with the casting ofnon-ferrous metals, such as aluminum, is the necessity that the materialhave sufficient physical strength. In casting non-ferrous metals, suchas aluminum, the insulating material that comes in contact with theelevated temperature of the molten metal is particularly susceptible tocracking and fracture; therefore sufficient physical strength andthermal dimensional stability are required of the insulating material.Additionally, in connection with the casting of non-ferrous metals, itis desirable that outgassing of the insulating material in contact withthe molten metal be minimized. Several variants and improvements of thetobermorite type and xonotlite type calcium silicate insulatingmaterials are known in the prior art which attempt to rectify theshortcomings of the fundamental tobermorite type and xonotlite typecalcium silicate insulating materials.

In the past, asbestos fibers had been utilized as a reinforcing fiber inmanufacture of calcium silicate insulating materials to providesufficient strength and toughness to the insulating material. Althoughsuch asbestos containing insulating materials performed well, the use ofasbestos fibers has been widely discontinued due to health andenvironmental concerns.

U.S. Pat. No. 5,073,199 to Krowl et al. discloses a tobermorite typecalcium silicate insulating material containing pitch based graphitefiber to provide toughness and strength to the insulating material.However, the incorporation of such graphite fiber and its associatedmaterial cost results in an appreciable increase in the cost of theresultant product.

U.S. Pat. No. 4,690,867 to Yamamoto et al. discloses a xonotlite typecalcium silicate insulating material with improved strength suitable fornon-ferrous metal casting wherein reinforcing carbon fibers are notuniformly distributed in the material thus having zones of varyingstrength. Use of the material disclosed in U.S. Pat. No. 4,690,867 formolten metal casting is often accompanied by undesirable outgassingwhich creates voids and contaminants in the resultant cast metal.

U.S. Pat. Nos. 4,773,470 and 4,897,294 to Libby, et al. disclose the useof delaminated vermiculite as a substitute for asbestos in thecomposition of a tobermorite insulating material suitable for use inmolten metal casting. Although the use of vermiculite as a substitutefor asbestos results in material with reduced thermal shrinkage incomparison to materials containing only wollastonite as the inorganicfiber, the machineability of the material is compromised.

As a final example of attempts of the prior art to rectify theshortcomings of the fundamental tobermorite type and xonotlite typecalcium silicate insulating materials, U.S. Pat. No. 4,144,121 toOtouma, et al. and U.S. Pat. No. 4,334,931 to Assumi, et al. disclosethe use of previously synthesized xonotlite crystalline material toprovide strength comparable to that of an asbestos containing board.However, manufacture of these calcium silicate insulating materials ismore costly, in that, an additional step is required to produce thexonotlite crystalline material that is incorporated with the startingmaterials.

Accordingly, it is the principle objective of the present invention toprovide an insulating material that is suitable for use in non-ferrousmolten metal casting that is lightweight with greater refractoriness, istough and resistant to high temperature cracking, and does not possessthe shortcomings of the prior art insulating materials.

An additional objective of the present invention is to provide anasbestos-free fire resistant, heat insulating, electrical insulating,and corrosion resistant material, that may be utilized in otherapplications in addition to non-ferrous metal casting, having reducedhealth exposure risk and minimal environmental impact.

Other objects and advantages of the present invention will be apparentto those skilled in the art from the following description of theinvention.

SUMMARY OF THE INVENTION

The present invention is an asbestos-free thermal insulating materialthat is resistant to high temperature cracking that is formed from amixture consisting essentially of, in parts by weight percentage: 12 to40 weight percent of lime, 12 to 40 weight percent of a siliceouscomponent, 0 to 70 weight percent of wollastonite, 10 to 70 weightpercent of alumina silica microspheres, and 0 to 10 weight percent oforganic fiber, in the presence of at least one part by weight water perpart by weight of the combined materials of the mixture other thanwater, to form an aqueous slurry; molding the aqueous slurry into ashape and expelling excess water; curing the molded shape underappropriate steam pressure for sufficient time to cause the limesiliceous component and water to react to form the desired tobermoriteor xonotlite hydrated calcium silicate matrix reinforced by the aluminasilica microspheres and wollastonite, if present; thereafter, the curedshape is dried, heat treated and machined to particular shape, ifdesired.

Should a pre-mold reacted process be employed to form xonotlite, theslurry formed in the forgoing mixture, is reacted under appropriatesteam pressure for sufficient time to cause the lime, siliceouscomponent and water to react to form the desired xonotlite hydratedcalcium silicate matrix; the slurry is then molded into a shapeexpelling excess water. Thereafter, the molded shape is dried andmachined to particular shape, if desired.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS

The principal components of the present invention are a calcium source,a siliceous component, alumina silica microspheres, wollastonite, ifdesired, and a small amount of organic fiber, if desired.

The calcium source may be any suitable hydrated lime or quick lime. Theamount of lime utilized by weight is from 12 to 40 percent, andpreferably from 14 to 20 percent, of the total weight of the componentsother than water.

The siliceous component utilized may be of any substantially puresources of silica such as silica, diatomaceous earth, silica fume,colloidal silica, or other suitable oxides of silicon. The amount ofsiliceous component utilized by weight is from 12 to 40 percent, andpreferably from 14 to 20 percent, of the total weight of the componentsother than water. The lime and siliceous component are utilized in aratio suitable for the desired formation of the tobermorite or xonotlitehydrated calcium silicate matrix that forms through the reaction of thelime, siliceous component and water under appropriate conditions.

The alumina silica microspheres are lightweight hollow sphericalparticles, extracted from pulverized fuel ash generated by coal firedfurnaces, such as those utilized in coal fired power stations, and arecomposed primarily of silica and alumina as their major components withsome iron oxides as a minor component. The melting point of the aluminasilica microspheres is above 2100 degrees Fahrenheit. As the aluminasilica microspheres possess such a high melting point, they areparticularly suitable for use in the calcium silicate based insulatingmaterial of the present invention and its applications includingnon-ferrous metal casting. Additionally, as the microspheres are hollow,the density of the resultant insulating material of the presentinvention is reduced and its refractoriness is increased. Further, asthe shells of the microspheres are remarkably strong, they are able toeasily withstand the rigorous mixing, pressing and treatment involved inthe process of manufacturing the reacted calcium silicate insulatingmaterial of the present invention.

Suitable-microspheres for use in the present invention are available,from the PQ Corporation under the trademark EXTENDOSPHERES and fromTrelleborg Fillite, Inc. under the trademark FILLITE, with variousgrades and sizes. The present invention is not critically sensitive tothe alumina and silica content of the various grades of microspheres;the alumina content of the various currently available grades ofmicrospheres range from 27 to more than 43 weight percent, and thesilica content ranges from 55 to 65 weight percent of the microspherestotal weight. The size of the microspheres is also not critical to thepresent invention; microspheres are currently available in the range ofabout 5 to about 500 microns in size, all of which are suitable. Aparticularly suitable microsphere, because of its relatively low cost,is EXTENDOSPHERES SG which is composed of 58 to 65 weight percentsilica, 28 to 33 weight percent alumina, and up to 4 weight percent ironoxides, with a mean particle diameter of 120 to 130 microns. The amountof silica alumina microspheres utilized by weight is between 10 and 70percent, and preferably from 10 to 30 percent, of the total weight ofthe components other than water.

Wollastonite is a crystalline form of anhydrous calcium silicate. In thepresent invention, the wollastonite, if used, preferably has a particlesize whereby 60 weight percent of its particles pass through a sieve no.50 mesh screen. The wollastonite, if used, is up to 70 percent, andpreferably from 30 to 50 percent, of the total weight of the componentsother than water.

An organic fiber may be incorporated to facilitate the handling andmolding of the insulating material of the present invention and toprovide green strength in the process of manufacture. The amount oforganic fiber utilized is up to 10 percent, and preferably from 4 to 8percent, of the total weight of the components other than water. Theorganic fiber may be wood fiber, polyester or other synthetic fiber,cotton or other natural fibers. Kraft, which is made from wood pulp isparticularly preferred.

To form a calcium silicate insulating material of the present inventioncontaining a predominantly and substantially pure tobermorite typehydrated calcium silicate matrix, the lime, the siliceous material, thealumina silica microspheres, the wollastonite, if utilized, and theorganic fiber, if utilized, are mixed in the presence of at least onepart by weight water per part by weight of the lime, siliceous material,alumina silica microspheres, wollastonite and organic fiber of themixture to form an aqueous slurry. Mixing occurs with such vigor and forsuch time as is necessary to thoroughly disperse the dry solid materialsthroughout the slurry. The aqueous slurry is then placed into a moldwhere excess water is pressed from the aqueous slurry to form a shaperetaining molded body. A typical shape of the molded body is a flat 4foot by 8 foot sheet about ½ to 4 inches thick. The molded body is thencured under high pressure steam for such time and at such pressure asnecessary cause the lime, siliceous material and water to react to formthe tobermorite calcium silicate hydrate crystalline matrix. Steampressure of about 100 psi for a period of about 24 to 32 hours has beenemployed to form a satisfactory tobermorite crystalline matrix; howeverother variations of time and steam pressure which are known in the artmay be employed.

The cured body may then be oven dried to about 250 degrees Fahrenheit toreduce its moisture content and subsequently heat treated to burn awayany organic fiber material that was utilized to facilitate handling andmolding and provide green strength for the manufacturing process.

To form a calcium silicate insulating material of the present inventioncontaining a predominantly and substantially pure xonotlite typehydrated calcium silicate matrix, the above components are used and theabove steps for forming the insulating material having a tobermoritetype hydrated calcium silicate matrix are followed with the exceptionthat the heat treatment step is eliminated and the molded body is curedunder high pressure steam for such time and at such pressure asnecessary to cause the lime, siliceous material and water to react toform the xonotlite calcium silicate hydrate crystalline matrix. Steampressure of about 200 psi for a period of about 15 to 20 hours has beenemployed to form a satisfactory xonotlite crystalline matrix; howeverother variations of time and steam pressure which are known in the artmay be employed.

Additionally, a calcium silicate insulating material of the presentinvention containing a predominantly and substantially pure xonotlitetype hydrated calcium silicate matrix may be manufactured by analternate method. In this alternate method, the lime, the siliceousmaterial, the alumina silica microspheres, the wollastonite, ifutilized, and the organic fiber, if utilized, are mixed in the presenceof at least one part by weight water per part by weight of the lime,siliceous material, alumina silica microspheres, wollastonite andorganic fiber to form a slurry, which is placed under high pressuresteam for such time and at such pressure as necessary to cause the lime,siliceous material and water to react to form xonotlite. Thereafter, thereacted aqueous slurry is placed into a mold where excess water ispressed from the aqueous slurry to form a molded body. The molded bodymay then be oven dried.

Some of the beneficial properties of the insulating material of thepresent invention are illustrated by way of the following non-limitingcomparative examples. In each of the following examples, insulatingmaterials of particular component formulations cured to a tobermoritetype hydrated calcium silicate crystalline matrix were prepared asfollows:

The components were mixed in the presence of water, which was utilizedin an amount greater than one part by weight of water per part by weightof the components other than water, to form an aqueous slurry.

The aqueous slurry was then transferred into a mold and pressed to 700psi, where the excess water was pressed from the aqueous slurry to forma green state flat sheet with the dimensions of 3 inches by 8 inches incomparative example 1, and 4 feet by 8 feet sheet in comparativeexamples 2 and 3. To ensure validity of comparison, test samples withineach comparative example were pressed within the same mold and press.

The molded sheet was then cured under steam pressure of 100 psi for 24hours causing the lime, siliceous material and water to react to formthe tobermorite calcium silicate hydrate crystalline matrix.

The cured sheet was then oven dried to 250 degrees Fahrenheit until itreached an equilibrium moisture constant.

Finally the sheet was heat treated to above 500 degrees Fahrenheit,thereby burning away the organic fiber, until the mass of the sheetreached equilibrium.

COMPARATIVE EXAMPLE 1

The following table sets forth the formulation variables in content ofwollastonite and alumina silica microspheres of seven test samples andtheir measured density, modulus of rupture (bending strength) andcalculated strength factor. The test samples were prepared with aformulation expressed in weight percent of the total components, otherthan water, of 17 percent hydrated lime, 17 percent silica flour, 6percent kraft and the remainder as alumina silica microspheres andwollastonite, with the microshpere content increasing in 10 percentincrements, as indicated in the table.

An important performance criterion for calcium silicate insulatingmaterial utilized in the casting of non-ferrous metals is its modulus ofrupture (bending strength). Consistently, a higher density material willyield a higher modulus of rupture. To properly evaluate the strengthcharacteristics of materials with different densities, a formula isemployed to normalize the impact of variation in density; a strengthfactor, which normalizes this variation and allows comparisons to bemade, is equal to the modulus of rupture (bending strength) divided bythe density squared.

COMPARATIVE EXAMPLE 1 TABLE test sample number 1 2 3 4 5 6 7microspheres 0 10 20 30 40 50 60 (in weight percent) wollastonite 60 5040 30 20 10 0 (in weight percent) density 65.0 52.1 47.6 44.1 42.5 33.136.8 (in lbs/ft³) modulus of rupture 1400 1067 1155 794 856 639 468(bending strength in psi) strength factor .33 .39 .51 .41 .47 .44 .35(MOR/D²⁾

From the table in this comparative example, it can be observed from testsample 1, which contains no microspheres, and test sample 3, whichsubstitutes 20 percent weight of microspheres for a corresponding amountof wollastonite, that the strength factor, which is normalized forvariations in density, can be increased by the substitution ofmicrospheres for wollastonite, while at the same time overall density isreduced. In comparison of test sample 1, containing no microspheres andtest sample 2 which substitutes only 10 percent weight of microspheresfor a corresponding amount of wollastonite, an appreciable increase inthe strength factor is observed with only a 10 percent by weightsubstitution of microspheres for wollastonite. Further, it becomesapparent from the test sample results, and in particular the results oftest sample 7, in which all of the wollastonite has been replaced bymicrospheres, that the microspheres in the present invention are boundto or are being tightly incorporated with the calcium silicate matrix.Typically, when density is reduced by incorporation of low densityinsulating materials, such as perlite and vermiculite, the strength ofthe material is reduced dramatically.

COMPARATIVE EXAMPLE 2

In this comparative example, a calcium silicate material test sample ofthe prior art, not containing alumina silica microspheres, was comparedto a similar test sample formulation of the present invention containingalumina silica microspheres. Both test samples were prepared with aformulation expressed in weight percent of the total components, otherthan water, of 17 percent hydrated lime, 17 percent silica flour, and 6percent kraft. In the test sample of the prior art material, theremaining 60 percent component was composed of wollastonite; and in thetest sample formulation of the present invention the remaining portionwas composed of 20 percent alumina silica microspheres and 40 percentwollastonite.

Three specimens from both samples were cut to dimensions of 1 inch by 1inch by 12 inches. The specimens were then conditioned at 250 degreesFahrenheit for 24 hours to normalize the specimens and remove anymoisture they may have accumulated. One specimen at a time was submergedin a liquid aluminum bath of a known alloy at a temperature of 1350degrees Fahrenheit so that the wetted end of the specimen was threeinches below the surface of the aluminum. The outgassing from thespecimen was observed as bubbles from the liquid aluminum. The durationthat the bubbles were observed, from the time of contact with the liquidaluminum to the cessation of the bubbles was recorded along with thesize of the bubbles observed.

Calcium silicate insulating materials, even when heat treated, exhibitsome amount of out gassing when exposed to liquid non-ferrous metals.This outgassing, or bubbling in the molten metal, is caused by theexpansion of the air that exists in the calcium silicate insulatingmaterial as it is taken from room temperature and exposed to moltenmetal. Minimization of outgassing is desirable to prevent contaminationof the cast metal and prevent injury from molten metal. The amount ofoutgassing from a calcium silicate insulating material can be evaluatedby observing the duration and size of bubbles exhibited when the calciumsilicate insulating material is immersed in molten metal, wherein it ispreferable to observe smaller bubbles and shorter duration.

The specimens from the test sample of the prior art were observed toexhibit outgassing effects of about 3 minutes duration with medium sizedbubbles, whereas the specimens of a formulation of the present inventionwere observed to exhibit outgassing effects for only about 2 minutesduration with medium sized bubbles.

COMPARATIVE EXAMPLE 3

In this comparative example, a calcium silicate material test sample ofthe prior art, not containing alumina silica microspheres, was comparedto a similar test sample formulation of the present invention containingalumina silica microspheres. Both test samples were prepared with aformulation expressed in weight percent of the total components, otherthan water, of 17 percent hydrated lime, 17 percent silica flour, and 6percent kraft. In the test sample of the prior art material, theremaining 60 percent component was composed of wollastonite; and in thetest sample formulation of the present invention the remaining portionwas composed of 20 percent alumina silica microspheres and 40 percentwollastonite.

The 4 foot by 8 foot sheet test samples were then cut into 32 1 foot by1 foot square specimens. The specimens were each weighed and measured inlength, width, and thickness to calculate the density in pounds percubic foot of each specimen. Thereafter the maximum variation withineach test sample was calculated.

It is desirable that calcium silicate insulating materials be uniformand consistent throughout. Consistency and uniformity of the insulatingmaterial increases its thermal shock resistance, resulting in greatercrack resistance when placed in contact with molten metal. Additionally,consistency and uniformity of the insulating material facilitatesmachining, and ensures consistent density of parts machined from a sheetof insulating material, irrespective of the origin location of thepre-machined blank within the sheet of the insulating material.

The maximum and minimum density measured from specimens of the prior arttest sample were 78.5 lbs/ft³ and 62.0 lbs/ft³ respectively. The priorart test sample therefore exhibited a measured variation in densitywithin the 4 foot by 8 foot sheet of 16.5 lbs/ft³. In comparison themaximum and minimum density measured from the specimens of the presentinvention test sample were 52.3 lbs/ft³ and 48.0 lbs/ft³ The presentinvention test sample therefore exhibited a measured variation indensity within the 4 foot by 8 foot sheet of only 4.3 lbs/ft³, adramatic increase in uniformity and consistency.

What is claimed is:
 1. A method for producing a calcium silicateinsulating material, including the steps of: a. molding a shape from anaqueous slurry of a mixture comprising: 12 to 40 weight percent lime, 12to 40 weight percent siliceous component, 10 to 70 weight percentalumina silica microspheres, 0 to 60 weight percent wollastonite, and 0to 10 weight percent organic fiber, all slurried in at least one part byweight water per part by weight of said mixture; b. curing said shape inan atmosphere of steam at sufficiently elevated pressure for sufficienttime to cause the lime, siliceous component, and water to form a calciumsilicate hydrate matrix. c. drying said shape to remove excess water. 2.A method for producing a calcium silicate insulating material as inclaim 1, wherein the amount of said lime of said mixture is 14 to 20weight percent, the amount of said siliceous component of said mixtureis 14 to 20 weight percent, the amount of said alumina silicamicrospheres of said mixture is 10 to 30 weight percent, the amount ofsaid wollastonite of said mixture is 30 to 50 weight percent, and theamount of said organic fiber of said mixture is 4 to 8 weight percent.3. A method for producing a calcium silicate insulating material as inclaim 2, further comprising the step of heat treating said shape toabove 500 degrees Fahrenheit.
 4. A method for producing a calciumsilicate insulating material as in claim 2, wherein the amount of saidpressure utilized and the duration of said time employed in the curingstep (b) result in a predominantly tobermorite phase of said calciumsilicate hydrate matrix.
 5. A method for producing a calcium silicateinsulating material as in claim 2, wherein the amount of said pressureutilized and the duration of said time employed in the curing step (b)result in a predominantly xonotlite phase of said calcium silicatehydrate matrix.
 6. A method for producing a calcium silicate insulatingmaterial as in claim 4, further comprising the step of heat treatingsaid shape to above 500 degrees Fahrenheit.
 7. A method for producing acalcium silicate insulating material, including the steps of: a.producing an aqueous slurry from a mixture comprising: 12 to 40 weightpercent lime, 12 to 40 weight percent siliceous component, 10 to 70weight percent alumina silica microspheres, 0 to 60 weight percentwollastonite, and 0 to 10 weight percent organic fiber, all slurried inat least one part by weight water per part by weight of said mixture; b.reacting said aqueous slurry in an atmosphere of steam at sufficientlyelevated pressure for sufficient time to cause the lime, siliceouscomponent, and water to form a calcium silicate hydrate matrix; c.molding said slurry into a shape; d. drying said shape to remove excesswater.
 8. A method for producing a calcium silicate insulating materialas in claim 7, wherein the amount of said pressure utilized and theduration of said time employed in the reacting step (b) result in apredominantly xonotlite phase of said calcium silicate hydrate matrix.9. A method for producing a calcium silicate insulating material as inclaim 7, wherein the amount of said lime of said mixture is 14 to 20weight percent, the amount of said siliceous component of said mixtureis 14 to 20 weight percent, the amount of said alumina silicamicrospheres of said mixture is 10 to 30 weight percent, the amount ofsaid wollastonite of said mixture is 30 to 50 weight percent, and theamount of said organic fiber of said mixture is 4 to 8 weight percent.10. A method for producing a calcium silicate insulating material as inclaim 9, wherein the amount of said pressure utilized and the durationof said time employed in the reacting step (b) result in a predominantlyxonotlite phase of said calcium silicate hydrate matrix.